Heretofore, two types of molds—one mold made of metal and the other mold made of non-metal material—have been used in an infusion/injection molding process for producing fiber-reinforced composite parts such as wind rotor blades or locomotive parts. Molds made of metals such as steel, aluminum, copper or metal alloy, provide superior surface temperature uniformity because of metal molds' higher thermal conductivity, but the metal molds are heavy and thus difficult to handle; and the metal molds of large and complex shapes are expensive to make.
On the other hand, non-metal molds such as fiber-reinforced composite molds are much lighter and can be made faster at lower cost, especially for large and complex geometries. The non-metal molds, however, often suffer from large temperature deviation (e.g., ±10% of average value) across the mold surfaces. The higher the mold temperature, the larger the deviation can occur across the whole mold surface due to, for example, (1) the utilization of resin-based composite materials with inhomogeneous and anisotropic laminate structures, and (2) the non-uniform heat generated by the heating wires in the heating layer. A large temperature deviation often (1) causes “hot-spots (e.g., +10% of average value)/cold-spots (e.g., −10% of average value)” at mold surfaces, (2) leads to large variation in resin viscosity, and (3) affects resin flow, which may cause dry spot formation in the finished parts. In addition, the non-uniform heating of thermoset materials enclosed in the mold may lead to improper curing and cause undesired deformation of the finished parts. A mold that can be used in an infusion/injection molding process for producing fiber-reinforced composite parts without the disadvantages described above would be advantageous in the art.
U.S. Pat. No. 5,260,014 discloses a method of making injection molds suitable for use in injection molding, structural foam molding, low-pressure injection molding, and gas-assisted injection molding of plastic articles. The injection mold contains an electrodeposited thin metal layer on the mold's outer surface, and a rigid thermoset plastic material is cast upon the inner surface of the metal layer for supporting the metal layer. Heat transfer elements are cast within the plastic material and located adjacent to the metal layer to transfer heat for the metal layer and the plastic material. U.S. Pat. No. 5,260,014 also discloses that the thin metal layer is nickel, the plastic material is epoxy, and the heat transfer elements are metal chips and heat transfer tubing. The following features exist in the mold described in the above patent: (1) the metal layer is electrodeposited on a mold blank; (2) the metal layer is deposited on the surface of a finishing mold; (3) the metal layer backing material is formed by casting; and (4) the heating elements are of a spot area type. Molds having the above features may not be suitable for making large area curved molds such as wind rotor blade molds; and, an electrodepositing process is not a cost-effective solution because the process normally involves submerging the part into a container or vessel which holds the coating bath or solution and applying direct current electricity.
U.S. Pat. No. 4,120,930 discloses a mold for shaping a material to be molded, wherein the mold is formed by casting a first mold base portion formed of a bulk material such as Portland cement, carbon, graphite or castable ceramic material and the like to define a mold cavity; and then coating the mold cavity with a first metallic layer. Then a second hard surface layer formed of a material such as the carbides, nitrides, and oxides of tungsten, titanium, boron, silicon and aluminum is deposited on the surface of the metallic first layer. The mold-forming method of the prior art includes forming the mold backing material by casting and the metallic layer is deposited via coating by spraying, electrolytically or electroless depositions in the prior art. Similar to the process of U.S. Pat. No. 5,260,014, the coating technique of the prior art may not be suitable for making large molds to achieve desired thickness tolerance at reasonable cost.
JP62257819A discloses a method for making an injection mold. JP62257819A discloses a casting apparatus for casting fiber reinforced material (FRP) which consists of a male mold and a female mold. The female mold part includes a plastic part with a metal covering layer and pipes through which heating medium flows and the metal covering layer and pipes containing heating medium ensure uniform temperature distribution at the mold surfaces. The mold-making method described in JP62257819A has the disadvantages of: (1) the metal layer used is laid at mold surface which may lead to undesired fast heat loss and early degradation of the metal layer due to chemical erosion and prematurely wearing out; (2) the heating medium only lists fluid heating that involves design, operation and maintenance complexity; and (3) the metal layer is not adapted to a perforated product.
U.S. Pat. No. 3,827,667 discloses a method for making heat transfer panels utilized in large molds. The construction of the panels includes the use of a relatively thin metal sheet or panel in combination with a bulk material such as ceramic material forming the major portion of the mold structure and providing the support for the sheet or panel material. In constructing the panels, a heat transfer passageway is formed within or between the sheet material and the backup material through which heat transfer fluid may be flowed. The prior art also disclosed simple methods for forming the heat transfer molds. The panel-constructing method described in U.S. Pat. No. 3,827,667 has the following disadvantages: (1) the metal sheet or panel is laid on panel surface; (2) the back layer bulk material is ceramics (such materials as Portland cement, various ceramic materials of known compositions which are castable, mortars and cellular plastics, mortars and the like); and (3) the heat transfer passageway is limited to fluid. JP5192931A discloses a method of forming a ceramic or metal layer on the entire surface of or a part of the surface of a mold material made of concrete by flame spraying. The flame spraying, mold-forming method described in JP5192931A has the disadvantages of having to flame-spray the metal layer onto the mold surface; and flame spraying involves melting raw materials to be deposited that produces a large amount of dust and fumes made up of very fine particles. Flame spraying also requires the utilization of spraying equipment and fuel gases. All of the above disadvantages create safety hazards. The complex method disclosed in JP5192931A simply involves an unsafe operation of inserting a metal layer into fabric preforms. In addition, the matrix material of this mold is concrete which is heavy compared to other lighter materials used for fiber reinforced laminates/sandwich structures. The method and mold disclosed in JP5192931A does not contain a heating system; and an external heating device is needed to infuse and cure composites made by the method. Also, a flame-sprayed layer prepared by the above method may be porous; and the porosity of the layer can create a non-uniform temperature distribution across mold surfaces.
WO2009007077A1 discloses an integrally heated ceramic mold for manufacturing polymeric composite materials, and a method of manufacturing such a mold. The mold is suitable for manufacturing relatively large components such as wind turbine blades, and the mold enables the profile of the heat output at a working surface of the mold to be accurately controlled to complement the component being molded. However, WO2009007077A1 has the following disadvantages: (1) the mold body is made from ceramic that is brittle and weak in tension and shearing; and the mold body may also have a porous mold surface; (2) the manufacturing process of the ceramic mold is complex and expensive; and (3) the mold does not incorporate a metal layer to enhance mold surface temperature uniformity.
The prior art references above similarly disclose utilizing a metal/ceramic layer on the outmost mold surface, i.e. above the outmost mold surface layer, in spite of the different materials and fabrication processes introduced. None of the processes of the prior art involves inserting a metal layer beneath the outmost mold surface layer.